1. Field of the Invention
The present invention relates to an angular velocity sensor, and more particularly to an angular velocity sensor for use in posture control of a movable object such as an aircraft and an automotive vehicle, a navigation system or the like.
2. Description of the Related Art
A well-known angular velocity sensor has a construction as shown in FIG. 7. FIG. 7 is a cross-sectional side view of the conventional angular velocity sensor.
The angular velocity sensor shown in FIG. 7 has a base block 1 on which a tuning fork portion (not shown) is firmly fixed and a plurality of terminals 2 are mounted, so that an output signal from the tuning fork portion is outputted to the exterior by way of the terminals 2. The tuning fork portion is housed in a space defined by the base block 1 and a cover 3.
The terminals 2 on the base block 1 are fixed spaced apart from each other on a first circuit board 4 by soldering. The first circuit board 4 is electrically connected to one end of a connection terminal 5. A second circuit board 6 is electrically connected to the other end of the connection terminal 5, with a processing circuit 7 constituted of an integrated circuit (IC) being provided on the upper surface of the second circuit board 6. The processing circuit 7 is adapted to process the output signal from the tuning fork portion.
Both ends of the first circuit board 4 are supported by a pair of rubber members 8. The rubber members 8 absorb vibrations so that a strong vibration from the exterior may not be directly applied to the tuning fork portion. A pair of support blocks 9 support the first circuit board 4 by way of the rubber members 8, and directly support the second circuit board 6. A casing 10 accommodates therein the base block 1, the cover 3, the first circuit board 4, the connection terminal 5, the second circuit board 6, the rubber members 8, and the support blocks 9.
An operation of the conventional angular velocity sensor having the above construction is described. The tuning fork portion flexes and vibrates at a velocity v with its predetermined natural frequency in its driving direction in response to application of an alternating current. In this state, when the tuning fork portion rotates at an angular velocity ω about a central axis thereof, a Coriolis force F=2 mv×ω generates in the tuning fork portion. An electric charge, which is generated in the tuning fork portion (not shown) by the Coriolis force, is amplified by the processing circuit 7 on the second circuit board 6. The amplified output voltage is measured by an external computer (not shown). Thus, the angular velocity of an object is detected. Japanese Unexamined Patent Publication No. 8-271257 discloses information reciting the conventional art relating to the invention, for example.
In the conventional arrangement, vibrations are absorbed by the rubber members 8 to prevent direct transmission of a strong vibration from the exterior to the tuning fork portion. Since the first circuit board 4 is supported by the rubber member pair 8, if the rubber members 8 are not properly fitted in the support blocks 9, the first circuit board 4 may likely be tilted, with the result that the tuning fork portion housed in the space defined by the base block 1 and the cover 3 may be tilted. Thereby, the output signal from the tuning fork portion may be diminished, and the output characteristic of the angular velocity sensor may be unstable.